Extreme events are more likely than we think. Taleb calls these "Black Swans" after the one-time European certainty, based on northern hemisphere experience, that all swans were white. Among the many examples he discusses are the start of World War I, the sales of the Harry Potter novels, and a turkey who spends a thousand days being well fed before being killed on the thousand-and-first day.

Taleb looks at some of the features of human psychology that make us poor at evaluating uncertainties and risks: confirmation biases, attraction to narrative explanations, epistemic arrogance, and tunneling. Other fundamental difficulties come from silent evidence, the general "problem of induction", and the nature of historical causation. And a specific issue in economics and the other social sciences is an insistence on using Gaussian distributions where they are not appropriate; here Taleb introduces the notion of Gray Swans, which we can get some grasp on using alternative tools such as fractal analysis. (The current Global Financial Crisis is a Gray Swan rather than a Black Swan.)

Taleb presents his ideas largely through narrative, anecdotes, and even a few fictional stories. This is a reasonable approach to presenting what is essentially a pragmatic way of looking at the world rather than any kind of formal system. One wonders, however, whether Taleb himself hasn't fallen victim to some of the very problems he raises — confirmation bias, attraction to narrative, and so forth. He also draws on the scientific and philosophical literature, drawing on a range of disciplines and sources, but doesn't go into any of it in depth. Given the heterogeneity of Black Swans, perhaps their deeper study will inevitably be domain specific.

Taleb is a quantitative analyst or "quant" himself and a hedge-fund manager, but he doesn't focus on finance in The Black Swan. His brief investment suggestion is a "barbell" portfolio, with 85 or 90 percent in Treasury Bills, as a defence against extreme negative events, and the rest spread across highly speculative investments such as small biotech companies, to try to catch a few extreme positive events.

There is a lot about Taleb, or "NNT" as he refers to himself, in The Black Swan. His opening example of a Black Swan, for example, is the civil war in Lebanon which disrupted his childhood, and most of his other anecdotes are also taken from his own experiences. Taleb has a high opinion of himself and a few other figures such as Mandelbrot, Hayek, Popper, Montaigne and Sextus Empiricus come in for praise. Otherwise a lot of people and institutions cop a hammering at his hands, from individual philosophers, bureaucrats and politicians to institutions, governments and academia generally. Taleb is particularly unhappy with Nobel Prizes and the Nobel Committee. (He mostly complains about the Economics prizes, but he also makes fun of the Literature awards, which seems strange because, while some of these have gone to predictable worthies, many have gone to unexpected writers from way outside the mainstream.)

I found all this more amusing than annoying — it helps that Taleb is erudite and shares some of my prejudices and dispositions — but the personalised presentation is likely to put some readers off and will distract from the ideas.

In any event, The Black Swan presents some very important ideas. Since it is also entertaining and easy to read, I recommend it to anyone curious about uncertainties and the way we approach them.

February 2009

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